A dual interface (DI or DIF) smartcard (or smart card; SC) may generally comprise:                an antenna module (AM) having a module antenna (MA) for contactless operation and contact pads (CP) for contact operation,        a card body (CB) having layers of plastic or metal, or combinations thereof, and        a booster antenna (BA) disposed in the card body (or “inlay”). Some examples of smart cards having booster antennas are disclosed in U.S. Ser. No. 14/020,884 filed 8 Sep. 2013 (US 20140091149, 3 Apr. 2014)        
The antenna module (AM), which may be referred to as a transponder chip module (TCM) or RFID module may generally comprise:                a module tape (MT) or chip carrier tape (CCT), more generally, simply a “substrate”;        a contact pad array (CPA) comprising 6 or 8 contact pads (CP, or “ISO pads”) disposed on a “face up side” or “contact side” (or surface) of the module tape (MT), for interfacing with a contact reader in a contact mode (ISO 7816);        an RFID chip (CM, IC) which may be a bare, unpackaged silicon die or a chip module (a die with leadframe, interposer, carrier or the like) disposed on a “face down side” or “bond side” or “chip side” (or surface) of the module tape (MT);        a module antenna (MA) or antenna structure (AS) disposed on the face down side of the module tape (MT) for implementing a contactless interface, such as ISO 14443 and NFC/ISO 15693 with a contactless reader or other RFID device.        
An antenna modules (AM) which may be able to operate without a booster antenna (BA) in the card body (CB) may be referred to as transponder chip modules (TCM), or as a transponder IC module.
The antenna module (AM) or transponder chip module (TCM) may be generally rectangular, having four sides, and measuring approximately 8.2 mm×10.8 mm for a 6-contact module and 11.8 mm×13.0 mm for an 8-contact module. Alternatively, the transponder chip module (TCM) may be round, elliptical, or other non-rectangular shape. When operating in a contactless mode, the antenna module (AM) or transponder chip module (TCM) may be powered by RF from an external RFID reader, and may also communicate by RF with the external RFID reader.
A module antenna (MA) may be disposed on the module tape (MT) for implementing a contactless interface, such as ISO 14443 and NFC/ISO 15693. Contact pads (CP) may be disposed on the module tape (MT) for implementing a contact interface, such as ISO 7816. The contact pads (CP) may or may not be perforated. The module tape (MT) may comprise a pattern of interconnects (conductive traces and pads) to which the RFID chip (CM, IC) and contact pads (CP) may be connected. The module tape (MT) may be “single-sided”, having a conductive layer (or cladding, or foil) on only one side thereof, such as the “face-up” side thereof, such as for the contact pads (CP). The module tape (MT) may be “double-sided”, having conductive layers (or claddings, or foils) on both sides thereof. A conductive layer on the “face-down” side of the module tape (MT) may be etched to form a module antenna (MA) having a number of tracks (traces) separated by spaces.
The module antenna (MA) may be wire-wound, or etched, for example:                The module antenna (MA) may comprise several turns of wire, such as 50 μm diameter insulated wire. Reference may be made to U.S. Pat. No. 6,378,774 (2002, Toppan), for example FIGS. 12A, B thereof.        The module antenna (MA) may be a chemically-etched planar antenna (PA) structure. Reference may be made to U.S. Pat. No. 8,100,337 (2012, SPS), for example FIG. 3 thereof.        The module antenna (MA) may comprise a laser-etched planar antenna (PA) structure (LES). Reference may be made to U.S. Ser. No. 14/281,876 filed 19 May 2014 (US 20140284386, 25 Sep. 2014), incorporated by reference herein.        
A planar antenna (PA) structure, or simply “planar antenna (PA)”, whether chemically-etched (CES) or laser-etched (LES) may comprise a long conductive trace or track having two ends, in the form of a planar spiral encircling the RFID chip on the face-down side of the module tape. This will result in a number of tracks (actually, one long spiraling track), separated by spaces. The track width may be approximately 100 μm. Generally, with laser etching, the track width and the spacing between tracks can be made smaller than with chemical etching, and the tracks themselves can be made narrower than with chemical etching.
The (two) ends of the module antenna (MA) may be connected, either directly or indirectly to corresponding terminals (LA, LB) of the RFID chip (IC, CM). For example, one or both ends of the module antenna (MA) may be connected to bond pads or interconnect traces on the face-down side of the module tape (MT), to which the terminals of the RFID chip (IC, CM) may also be connected.
Alternatively, one or both ends of the module antenna (MA) may be connected via electrically conductive structures, which may be referred to as “contact bridges” or “connection bridges”, disposed on the face-up side of the module tape (MT), and which may be formed from the same conductive layer as the contact pads (CP). Some examples of connection bridges may be found in                US 20130146670 (2013-06-13, Grieshofer et al; “Infineon”)        US 20150129665 (2015, Finn et al.)        
The antenna (or antenna structure AS) may be laser etched from a copper layer (cladding or foil), which may have a thickness of approximately 18 μm-35 μm, but may be approximately 12 μm, which may be less than the skin depth of copper (18 μm), forming a number of tracks separated by a distance approximately equal to the width of the laser beam, such as approximately 25 μm. Subsequent to laser etching, the antenna structure may be plated, which may reduce the distance between tracks to approximately 20 μm (for example). This may result in increased performance of the antenna structure, and the overall antenna module AM (or transponder chip module (TCM)), and reduce performance constraints on the performance of a booster antenna (BA) in the card body (CB) of the smartcard (SC).
A module antenna (MA) connected to an RFID chip (CM), typically on a substrate or module tape (MT), may be referred to as a “transponder”. Generally, such a transponder may be a “passive” transponder which does not have its own power source (e.g., battery), but rather which receives (harvests) its operating power from an external reader (interrogator) rather, for example, from a battery. An “active transponder” may have its own internal power source, such as a battery.
Transponder chip modules (TCM) which are passive transponders may have an “activation distance” which may refer to the distance from an external reader at which the transponder may commence operation (turn on), and may also have a “read/write” distance which may refer to the distance from an external reader at which the transponder may communicate effectively and reliably, in both directions, with the reader.
Activation and read/write distances of at least a few centimeters (cm) are desirable. However, conventional antenna modules (AM) may require a booster antenna (BA) in a card body (CB) to achieve these distances. The transponder chip modules (TCM) disclosed herein may be capable of greater activation and read/write distances, without requiring a booster antenna (BA).
Some terms which may be used herein may include:                “skin depth” relates to the “skin effect” which is the tendency of an alternating electric current (AC) to become distributed within a conductor such that the current density is largest near the surface of the conductor. A “skin depth”, or minimum thickness for conducting current may be defined, for a given material at a given frequency. For example, at 13.56 MHz, the skin depth for copper may be approximately 18 μm (17.7047 μm).        “transparency” refers to the ability of electromagnetic radiation to pass through a material. A threshold for non-transparency (or the ability to interact with RF) may be a fraction of the skin depth for the metal layer in question at a given frequency of interest. For example, the non-transparency threshold for copper at 13.56 MHz, may be one-tenth of the skin depth, or approximately 1.7 μm.        